## Friday, 25 March 2016

### Python Operators

Operators are special symbols in Python that carry out arithmetic or logical computation. The value that the operator operates on is called the operand. For example:
``````
>>> 2+3
5``````
Here, `+` is the operator that performs addition. `2` and `3` are the operands and `5` is the output of the operation. Python has a number of operators which are classified below.

## Arithmetic operators

Arithmetic operators are used to perform mathematical operations like addition, subtraction, multiplication etc.
Arithmetic operators in Python
OperatorMeaningExample
+Add two operands or unary plusx + y
+2
-Subtract right operand from the left or unary minusx - y
-2
*Multiply two operandsx * y
/Divide left operand by the right one (always results into float)x / y
%Modulus - remainder of the division of left operand by the rightx % y (remainder of x/y)
//Floor division - division that results into whole number adjusted to the left in the number linex // y
**Exponent - left operand raised to the power of rightx**y (x to the power y)
Here is an example.
``````
x = 15
y = 4
print('x + y = ',x+y)
print('x - y = ',x-y)
print('x * y = ',x*y)
print('x / y = ',x/y)
print('x // y = ',x//y)
print('x ** y = ',x**y)``````
Output
```
x + y =  19
x - y =  11
x * y =  60
x / y =  3.75
x // y =  3
x ** y =  50625
```

## Comparison operators

Comparison operators are used to compare values. It either returns `True` or `False` according to the condition.
Comparision operators in Python
OperatorMeaningExample
>Greater that - True if left operand is greater than the rightx > y
<Less that - True if left operand is less than the rightx < y
==Equal to - True if both operands are equalx == y
!=Not equal to - True if operands are not equalx != y
>=Greater than or equal to - True if left operand is greater than or equal to the rightx >= y
<=Less than or equal to - True if left operand is less than or equal to the rightx <= y
Here is an example.
``````
x = 10
y = 12
print('x > y  is',x>y)
print('x < y  is',x<y)
print('x == y is',x==y)
print('x != y is',x!=y)
print('x >= y is',x>=y)
print('x <= y is',x<=y)``````
Output
```
x > y  is False
x < y  is True
x == y is False
x != y is True
x >= y is False
x <= y is True
```

## Logical operators

Logical operators are the `and``or``not` operators.
Logical operators in Python
OperatorMeaningExample
andTrue if both the operands are truex and y
orTrue if either of the operands is truex or y
notTrue if operand is false (complements the operand)not x
Here is an example.
``````
x = True
y = False
print('x and y is',x and y)
print('x or y is',x or y)
print('not x is',not x)``````
Output
```
x and y is False
x or y is True
not x is False
```
Here is the truth table for these operators.

## Bitwise operators

Bitwise operators act on operands as if they were string of binary digits. It operates bit by bit, hence the name. For example, 2 is `10` in binary and 7 is `111`.
Let x = 10 (`0000 1010` in binary) and y = 4 (`0000 0100` in binary)
Bitwise operators in Python
OperatorMeaningExample
&Bitwise ANDx& y = 0 (`0000 0000`)
|Bitwise ORx | y = 14 (`0000 1110`)
~Bitwise NOT~x = -11 (`1111 0101`)
^Bitwise XORx ^ y = 14 (`0000 1110`)
>>Bitwise right shiftx>> 2 = 2 (`0000 0010`)
<<Bitwise left shiftx<< 2 = 42 (`0010 1000`)

## Assignment operators

Assignment operators are used in Python to assign values to variables. `a = 5` is a simple assignment operator that assigns the value 5 on the right to the variable a on the left. There are various compound operators in Python like `a += 5` that adds to the variable and later assigns the same. It is equivalent to `a = a + 5`.
Assignment operators in Python
OperatorExampleEquivatent to
=x = 5x = 5
+=x += 5x = x + 5
-=x -= 5x = x - 5
*=x *= 5x = x * 5
/=x /= 5x = x / 5
%=x %= 5x = x % 5
//=x //= 5x = x // 5
**=x **= 5x = x ** 5
&=x &= 5x = x & 5
|=x |= 5x = x | 5
^=x ^= 5x = x ^ 5
>>=x >>= 5x = x >> 5
<<=x <<= 5x = x << 5

## Special operators

Python language offers some special type of operators like the identity operator or the membership operator. They are described below with examples.

### Identity operators

`is` and `is not` are the identity operators in Python. They are used to check if two values (or variables) are located on the same part of the memory. Two variables that are equal does not imply that they are identical.
Identity operators in Python
OperatorMeaningExample
isTrue if the operands are identical (refer to the same object)x is True
is notTrue if the operands are not identical (do not refer to the same object)x is not True
Here is an example.
``````
x1 = 5
y1 = 5
x2 = 'Hello'
y2 = 'Hello'
x3 = [1,2,3]
y3 = [1,2,3]
print(x1 is not y1)
print(x2 is y2)
print(x3 is y3)``````
Output
```
False
True
False
```
Here, we see that x1 and y1 are integers of same values, so they are equal as well as identical. Same is the case with x2 and y2 (strings). But x3 and y3 are list. They are equal but not identical. Since list are mutable (can be changed), interpreter locates them separately in memory although they are equal.

### Membership operators

`in` and `not in` are the membership operators in Python. They are used to test whether a value or variable is found in a sequence (string, list, tuple, set and dictionary). In a dictionary we can only test for presence of key, not the value.
OperatorMeaningExample
inTrue if value/variable is found in the sequence5 in x
not inTrue if value/variable is not found in the sequence5 not in x
Here is an example.
``````
x = 'Hello world'
y = {1:'a',2:'b'}
print('H' in x)
print('hello' not in x)
print(1 in y)
print('a' in y)``````
Output
```
True
True
True
False
```
Here, `'H'` is in x but `'hello'` is not present in x (remember, Python is case sensitive). Similary, `1` is key and `'a'` is the value in dictionary y. Hence, `'a' in y` returns `False`.